U.S. District Judge Lynn Adelman ruled Tuesday that the 2011 law discriminated against racial minorities and violated the 14th Amendment to the U.S. Constitution, as well as the 1965 Voting Rights Act, reports the New York Times. Adelman found that the law disproportionately impacted poor people, particularly African-Americans and Hispanics, and placed an unjustified burden on their constitutional right to vote.

“I find that the plaintiffs have shown that the disproportionate impact of the photo ID requirement results from the interaction of the requirement with the effects of past or present discrimination,” Adelman wrote in the decision (PDF). “Blacks and Latinos in Wisconsin are disproportionately likely to live in poverty. Individuals who live in poverty are less likely to drive or participate in other activities for which a photo ID may be required (such as banking, air travel, and international travel) and so they obtain fewer benefits from possession of a photo ID than do individuals who can afford to participate in these activities.”

The law, which was passed by a Republican-controlled legislature and signed into law by Republican Governor Scott Walker, also prohibited voters from using a college ID or veterans ID card. The stated purpose of the law was to prevent voter fraud. However, as Adelman pointed out in his opinion, the state was unable to show a single instance of voter impersonation or fraud at trial.

“If it is occurring in Wisconsin to any significant extent, then at trial, the defendants should have been able to produce evidence that it is,” wrote Adelman in his opinion. “The absence of such evidence confirms that there is virtually no voter-impersonation fraud in Wisconsin.”

Adelman also turned aside the state’s argument that it had an interest in promoting the integrity of the voting process, saying that voter ID laws actually undermine confidence in the electoral process.

The decision is the latest blow to the wave of voter ID laws that have been enacted since 2011. Since January alone, voter ID laws in Wisconsin, Arkansas and Pennsylvania have been struck down as unconstitutional, reports the Times.

Adelman’s opinion covered two cases that were not consolidated but were tried at the same time. The first case was filed by the Wisconsin chapter of the American Civil Liberties Union in 2011 challenging the constitutionality of the law. “This is a warning to other states that are trying to make it harder for citizens to vote,” Dale Ho, director of the ACLU Voting Rights Project, said in a statement to the Huffington Post. “This decision put them on notice that they can’t tamper with citizens’ fundamental right to cast a ballot. The people, and our democracy, deserve and demand better.”

The second case was filed in 2012 by attorneys at Arnold & Porter. For the firm, it marked their second victory this year in the voter ID realm, following its successful effort to knock out Pennsylvania’s ID law in January. Lead partner John Ulin told the ABA Journal that, unlike the ACLU’s lawsuit, his suit centered around violations of the Voting Rights Act. Ulin says that his team looked at previous voter ID cases and realized that those plaintiffs had lost, in large part, because of their failure to create a sufficient factual record.

“We wanted to make sure this judge had the factual record he needed to understand why this law violated the Voting Rights Act,” Ulin says. To that end, Ulin and his team put on several witnesses who had trouble getting the required identification, as well as a number of experts who demonstrated that voter-impersonation fraud was a myth and that the law was designed to prevent minorities from voting. “Based on voter records and driver’s license records, there are over 300,000 eligible voters in Wisconsin that do not have a qualifying identification that would allow them to vote,” Ulin says. “That’s nine percent of the eligible voters in the state, and a disproportionate number of them are black or Latino.”

Wisconsin attorney general J.B. Van Hollen, who represented the state, promised to appeal the decision. Meanwhile, Robin Vos, the Republican speaker of the State Assembly, told the Times that Adelman, a Democrat who was appointed to the bench by Bill Clinton, acted politically. “He used his personal bias to say that voter ID is just wrong,” Vos said. “Our intention was never to make it hard to vote. All we want to do is make sure we have some reasonable proof that people are who they say they are.”

Ulin, meanwhile, hopes that this decision will influence other pending challenges to voter ID laws, particularly in Texas and North Carolina. He is also confident that Adelman’s decision will survive an appeal. “The level of detail in Adelman”s opinion makes this a very strong case,” says Ulin.

Related article:

ABA Journal: “With the Supreme Court’s OK, states begin imposing new laws to limit the vote”

Updated at 4:49 p.m. to add comments from one of the attorneys involved in the case.